Wrap-stretch means



Dec. 7, 1954 G. E. LARsr-:N 2,696,241

4 WRAP-STRETCH MEANS Filed .July s. 195o y 5 shQessheet 1 /f/s ern-wf Irl-amar Dec. 7, 1954 G. E. LARsEN WRAP-STRETCH MEANS 5 sheets-sheet 2 med .my a, 195o Dec. 7, 1954 G'. E. LARsEN WRAPLSTRETCH MEANS 5 Sheets-Sheet 3 Filed July 3. 1950 United States Patent() WRAP-STRETCH MEANS George E. Larsen, Hawthorne, Calif., assignor to Northrop Aircraft, Inc., Hawthorne, Calif., a corporation of California Application July s, 195o, serial No. 171,852

3 Claims. (Cl. 15s-4s) The present invention relates to wrap-stretch forming of thin sheets and more particularly to a means and method of wrap-stretching thin sheets to form channelled parts that are closed to relatively small dimensions. The invention is particularly adapted for the production of thin leading edge skins for aircraft wing and tail surfaces, or the like, and for curved edges such as might be used around jet engine inlets on airplanes.

It is an object of the present invention to provide a means and method of forming thin sheets into parts having U-shaped sections, particularly when the open ends of the parts are relatively closely spaced.

It is another object of the invention to provide a means and method of forming deep U-shaped channels from sheet metal in which the lips of the channels are simultaneously formed to a desired curve.

It is a further object of the present invention to provide a means and method of forming U-shaped channels from sheet metal when the extent ,of the channel is curved.

It is still a further object of the invention to provide a means and method of forming U-shaped channels from sheet metal by which the channel metal is progressively stretch hardened.

And it is still another object of the invention to provide a means and method of forming U-shaped channels of sheet metal that are stretch hardened only after being formed to shape.

Briefly as to method, the invention comprises gripping a metal sheet by opposite edges thereof so thatv these edges can freely move toward each other over controlled arcs. The nose of a die of the desired contour is then applied intermediate the gripped edges and moved toward the sheet to Wrap the sheet around the die, the gripped edges moving freely toward the die under the urge of the gie cllintil the sheet is Wrapped around and conforms to Die movement is then continued, rst stretching lthe metal areas having the least die friction, this stretching progressing toward areas having greatest die friction. Die movement is continued until all of the metal is stretched and set to desired shape. U-shaped channels of any useful depth can be made by this process with the open ends of the channels spaced as little as one-half inch, if desired.

Briefly as to apparatus, means are provided to grip opposite edges of a metal sheet, these gripping means being mounted on'spaced hinged arms to swing freely toward each other over predetermined arcs. A ram, such as appears on a hydraulic brake, is provided with an end die of the desired shape, and means are provided to force the die against the sheet intermediate the gripping means to wrap the sheet around the die. After the sheet has been wrapped around the die, relative movement of the die and sheet is continued to stretch and set the metal of the wrapped and formed sheet. If it is desired that the areas of the sheet adjacent the gripping means be contoured in a reverse curve, secondary dies can be provided on the arms adjacent the gripping means.

Other objects, advantages and features of the present invention will be found by reference to the ensuing' description of the drawings in which:

Figure l is a perspective view, somewhat diagrammatic, of one preferred form of apparatus for forming leading edge skins for use in airplanes, in accordance with the present invention.

Figure la is a perspective view on a small scale, showina a power brake equipped with the apparatus of Figure 1..

Figures 2 and 3 are cross sectional diagrammatic views of the device of Figure 1 showing sheet suspension prior to wrap, and final wrap, respectively.

Figures 4 and 5 are schematic cross sectional views showing sheet position before and after wrap, respectively, of a device modified to contour the lips of the formed channel. o

Figure 6 is a cross sectional view of a sheet gripping means used on the device of Figure 1 taken as indicated by line 6-6 in Figure l.

Figure 7 is a cross sectional View of the sheet gripping device taken as indicated by the line 7 7 in Figure l Figure 8 is a schematic perspective view showing how a curved channel can be formed in accordance with the present invention.

Figure 9 is a diagrammatic perspective View showing the base of the forming machine for another embodiment wherein tapered channels are formed.

Figure 10 is a diagrammatic plan view of the apparatus in Figure 9, on a smaller scale, showing convergence of the hinge lines of the work holders.

Referring first to Figures l and la, a straight ram 1, such as may be found on a 600 ton hydraulic brake 2 for example, is provided with a primary die 3 held thereon by an extended key 4. Die 3 is externally contoured, for example, to form a leading edge for an airplane wing, and is made as long horizontally as desired, within the capacity of the brake. As shown in Figure 3, die 3 has a rounded nose 3a, and curved faces that curve smoothly rearwardly from the nose and terminate at a heel portion 3b near the base of the die in such manner that vertical transverse sections through the die show that the rearward terminal portions of the side faces extend in generally parallel direction. As shown in the drawings, the die is of considerably greater depth than thickness.

The bed plate 6 of the brake is provided with two spaced parallel and aligned rows of jaw bearings 7 passing around hinge pins 8 at the lower ends of two rigid jaw arms 9, both jaw arms being in this case alike. Hence, the axes of the pins 8 are in a common plane perpendicular to the path of movement of the die 3. The axes of the pins 8 are also symmetrically arranged with respect to the die 3 and are spaced apart along their length at distances at least as large as the corresponding major thicknesses of the die 3.

Each jaw arm 9 comprises a plate 10 as long or longer, for example, than primary die 3, reinforced by side ribs 11. Outwardly each arm 9 terminates in a gripper bar 12, these bars being parallel to the extent of the ram 1 and prlmary die 3. Jaw arms 9 are at all times respectively free to swing without restraint about the axes of thelr hinge pins 8 between generally horizontal and vertical positions.

Each gripper bar 12 is provided with a sheet gripping assembly best shown in Figures 6 and 7. Here, the gripper bar 12 is provided with a longitudinal groove 15 having converging side inserts 16 in which are inserted a pair of longitudinal wedges 17 running the full length of the bar 12 and shaped to slide in groove 15 from an extended position Where hardened and serrated facing surfaces 18 of the wedges 17 are in Contact, to a retracted posltlon where the inner surfaces 18 are spaced. A plurality of longitudinal rollers 20 are inserted between each wedge 17 and the side inserts 16, on which it moves, to facilitate such movement. In this embodiment. the surfaces 18 extend generally parallel to their plates 10.

As shown in Figure 7, at intervals along the extent of the gripper assemblies, air cylinders 21 are provided having pistons 22 bearing against the inner surfaces of wedges 17 to force the wedges outwardly in groove 15 to close. The Wedges are spread, or opened, by springs 23 operating through tension rods 24 engaging the inner portions of wedges 17, as shown in Figure 6. During movement of the wedges, rollers 20 are maintained in place by spring operated push rods 25 bearing against the top roller of each group thereof. It is convenient to place air cylinders 21, opening springs 23 and push rods 25 in groups spaced uniformly along gripper bars 12, as indicated in Figure l. All of the air cylinders 21 are :provided with exible air hoses 27, and are connected to an air pressure source through a control valve (not shown)l for simultaneousoper-ationv on'- each-jaw-arm- 9: f

When leading edge channels of U-shaped sections are to be formed, when the lips or legs of the U channel are not' to: be.- specially.A formed,L the; Wedges; are positioned'. in thegripper bars. so that: wherr the arms .-9 are' rotated' apart, as shown in Figure.2-theywilll receive,-.wthout: substantiall bending,v the; oppositey edges-1 oh as metall Vsheet 30to.-be= wrap-stretched.,y

With the4 Wedges1f7r closed; on the. sheetzedges by air pressure, the sheet will be suspended, with a slightzbelly therein, `in.` space. between the. two arms, below `ram 1 withitsz attached, primarydie- 3;` T he 4amount-pf belly will of course depend on the width ofthe sheet, the ram` stroke lengthr` and the amountof: final' stretch desired. Normally,` the sheet -will be wide: enough zto spread: thearm 9 so; thatdthe planes1,.containing= thelatteny eXtendf atta substantially obtuse` angle.;

With the sheet suspended, as shown in FigurexZ, theram: 1- isA loweredl or advanced fromiitsrretracted position and, the nose 3avv of-` the4 primary die'. 3 will contact thev sheet. Further lowering orA advancing of the die 31willforce'the sheet downwardly,thereby. swinging the arms 9 toward thet primary die 3 until'thesheet is fully. wrapped around the primary die asrshown in Figure :31. During-this@r wrapgthe arms are not driven-in any way, exceptr bythe pullof the sheet, nor is the material. stretched. Fullwrap is'obtained before stretchingbegins.

After the-.full wraphasbeen attained at a first advancedv position: of the die', the; ram with itsvattachediprimarydie is moved downwardly an' additional distance to a second advanced position to stretch the metal. This stretching will begin inthe meta'l between the. wedges: andthe heeli 3b of the primary die 3f. As this metal stretches, it hardens and resists further stretching; the unstretched metal beyond then stretchingagainst the frictional resistance ofthe primary die contact.. Inthis manner/the rnetal isprogressively stretched until. all of the original kmetal is stretched, even aroundthe nose 3a-of the primary die. After they enti'reformed channel' has thusbeen stretched andf hardened, the ram 1 is retracted, air pressure is cut off from cylinders 21, thegwedgesscparate, and-thet formed part iszremoved.

When it is desired' that' the lips or edge areas of the` channel be contoured, a modifiedv structure-asrshowna in Figures 4-and 5 is utilized- Here,tthe wedge-cavities opentoward each other, i. e'. thel gripping` surfaces-128 are gen-- erally perpendicular to thev plane off their corresponding arms 9 and secondary lip contouring dies 311 are positioned' on arms 9 so-that when the sheet'30'tobe wrap-stretched is clamped between the wedgesf 117', with the sheet in agenerallyv horizontal position, the edgeareas of the sheet are draped across the: secondary dies 31T, as` shownf in Figure-4. The-primary diev 3;. which in' this case can be as. narrow as desired, isthen forced against the sheet as previously described After the ram has been loweredt to'- obtain a complete wrap over both primary an'dfsecondar-y dies, with the arms` 9moving' freely toWardfthe-pr-imary die and engaging the sheet between the' latter andthe secondary dies, due to primary die pressureon the sheet, asshown in` Figure 5; additional. downward movement` of the ram causes thesheet material'to stretch; thisstret'ch` starting at areas of least die friction' and spreading pro-A gressively to areas ofhigher'fri'ction until the entirepa-rt has been stretchedand hardened. The ram` i'sv then'raised' and the formed, hardenedr part is= removed' with the channel lips contoured and stretch hardenedi Deep channels, with the sides thereof' spaced' as little" as one-half inch, can be formed in thismannerifv desired Channels tapered in thicknessI along their extent` can readily beformed by proper lengthwise taper oft primary die 3. ln this case, a corresponding convergenceV oftheK hinge lines is preferred. The latter embodiment istshown; in Figures 9 and l0 (die` andr-amomitted), wherein-thehinge pins 8, and therefore theplates 1.0,.converge at-.anangle X, and the U-shaped-channel 3.00 formed frornthe. metal sheettapersin thickness fromvadimensionA.atone, end to a lesser dimension B' at the. other end. For, this. embodiment, the metal sheet to. be inserted into the gripper assemblies has a trapezoidalshape;

Curved channels can also be readily. formedgvas shown in Figure 8, and,.if desired, the lips of the channels can be asymmetrical in shape and contour. InFigure 8, the secondary dies 31 are made to have different -curvatures and different eX-tents away from the channel sides'. In-

plan-form, one of the dies 31 has a convex curvature as cave curvature as indicated by numeral 33. Die 3 has sides curved along their length to fit between secondary dies 31, and, if desired, the primary die 3 may have an asymmetrical nose 3a. The forming procedure is the same as has been previously,l described, the part being first wrapped and thenstretched, ,although in this instance a complete wrap over'the secondary fdies cannot always be. made, untilatteind-stretching,l has started dueto. they diiferingextent ofthesecondarydies from the wedges 17.V

From the above description it will be apparent that there is thus provided a device of the character described possessing?v the: particular.; featuresv of:- advantage before enumerated as desirable, but which obviously is susceptible of modification imite-form,- propor-tions-, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While. inA order' to`-comply1y withi thestatute; the'v inventionr hasbeen described! in': language more orlessr specific as-- tot structuralLfeatures'-, it isztog-be understood` thatrtheinvention is Inotxlimited` to ythe specifi-c featuresshown', but that the mea-ns. and.constructionvherein disclo'sedi comprise thezprcferredfor-m ,ofi severalmodes ofi putting the inven-V- tion.- into effect; and-,the inventionfisg therefore; claimed' in any of its forms or modifications-:Within the legitimate andfvalidiscope ofthe appended claims.

What islclaimedisf l.A Apparatus for: forming` and. wrap-stretching afiat sheet metal blank intorazthin: structural channel of gen-- erallyI U-shapedi section `having considerably greater: depth than width;.compr-ising: 4an elongatedathin primaryfformf ing` die substantially Ueshapeda in, cross-section andi of? considerably greater depththanw-thickness, said die-.havinga curved noseand sidefaces thatf curvev smoothly rearwardlyi from'. saidrnoseI in,y such manner that' transverse sections-.through` the die-show the rearwardfterminal por-v tions. ofsaidf faces extending in. generally parallel directions; means :fory moving said' die rectilinearly from a retractedzto advanced-first and secondl positions; a bed plate; a pair of rigid jaw arms mounted forI unrestrained pivotal movement about: the corresponding axes'of-r a-pair of' stationary hinges secured' to t said` plate; said axes'- beingl disposed-2in1 a` commonl plane perpendicular toy the' path; of movement of said die and positioned in--spacedlopposi4- tion'` -toz saiddie'- nose'- insaid secondn position of-'said die, and said' axes being-v generally symmetrically arranged with-respect to saiddie andfspacedapart-along-their length -at distances att least" as` large asL thel corresponding majorA thicknesses of' saidV die; and' means `mounted onI said jaw arms*` remote from"V said hinge axes for-I gripping opposite' edgesr ofa. fiat4 sheet' metall blank of sufiicient dimensionl between'- itsf said edges-'to spread saidfjawarmsapart so` .that the planes containing said arms extend at a substanetially vobtuse included angle` therebetween,- said die in advancing; from said retracted-position to saidfirst` position. being effective-to contactv the blank' intermediate itsv said edges and thus pivotally move said arms toward'ea'chi other to'wrap Athey blankabout' said'die-nose and'side faces and`l conformz the blanhtot the configuration of-` said' die,

and said die in' advancing from said'rst'to saidsecond position: beingl effective to stretch said'V blank ybeyond its elastic-limit'. 1

2;. Thestruct'uredenedfin claim' l', in which the effectiveblankengaging surfaces ofl'the gripping means'arcv disposed generally parallelto the jaw arms;

36 The structure definediii claiml', in which the-effec tive blankfengaging surfaces of they grippingl meansare disposed; generally` perpendicular toV the jaw arms and' include aisecondarydie on at' least? one jaw arm adjacent the gripping-means thereon and-opposed* to the other jaw arm', saidsecon'dary'die beingl adapted to engage the face of' the blankl opposite: that engaged by the primary die, withthe-blanh'being engaged' between said pri'rnary'and secondary dies in thev rst position of the former.

ReferencestGited in the file of this patent UNITED,y STATES', PATENTS,

Number 1 1 Name- Date l-,O-iOSQfy 'Edding-' Nov. 19, 1912'- 1,461,471 Bancroft July lO, 19213 1-,622;5901= Jolstad Mar: 29;` 1927 4 (Other references on following page) Number 5 UNITED STATES PATENTS Name Date McLeod May 2, Longren July 2, Wetfstein June 20, May Oct.l 26, Flowers Apr. 11, Seifried Mar. 13, Lermont June 19, Jager June 19, Glud Jan. 6, Greene Mar. 2, Lindsey Mar. 2,

Welser Apr. 27,

Number Number Name Date Calrns May 4, 1948 Fields May 25, 1948 Cah111 June 22, 1948 Block June 28, 1949 Mayne Dec. 13, 1949 Green Oct. 24, 1950 Vaughn Oct 14, 1952 FOREIGN PATENTS Country Date Great Britain Apr. 5, 1938 Great Britain Feb. 6, 1942 

